{
  "port": 2021,
  "protocol": "tcp",
  "service": "servexec",
  "oneLiner": "Registered as servexec (xinuexpansion1 on UDP); no current standard service.",
  "whatItIs": "IANA registers 2021/tcp as servexec and 2021/udp as xinuexpansion1, another pair of undocumented early registrations. Nothing maintained implements them. Because it sits one digit above the FTP control port, 2021 is also a common manual choice for an alternate FTP or SFTP listener, so fingerprint rather than assume.",
  "exposure": {
    "verdict": "careful",
    "note": "If it turns out to be FTP moved off 21, that is cleartext authentication and should be never — replace it with SFTP or FTPS."
  },
  "checkCommand": "nc -vz TARGET 2021",
  "links": [
    {
      "title": "IANA port registry — 2021 (servexec)",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=2021",
      "kind": "iana"
    }
  ]
}